Electrical discharge machining assemblies and methods for using the same

ABSTRACT

EDM assemblies mount on a machining surface and discharge rotating sub-electrodes against the surface. The sub-electrodes can also revolve about another shared axis while discharging. Rotation and revolution may be achieved with planetary gears fixed with the sub-electrodes and meshing with a stationary sun gear. Several sub-electrodes can be used in a single assembly. Downward movement of the sub-electrodes from a central shaft on the mount allows several inches of the surface to be machined. Assemblies are usable in a nuclear reactor during a maintenance period to machine a hole for a replacement manway cover underwater in the flooded reactor. The differing rotational movements and vertical movement can be independently controlled with separate motors in the assembly. Power and controls may be provided remotely through an underwater connection.

BACKGROUND

FIG. 1 is a perspective view of a related art rotating electrode 10useable in electrical discharge machining (EDM). Typically, in nuclearreactor environments and other industrial settings, it is necessary toremove materials, such as by making holes, in underwater or remotestructures. For example, in a nuclear reactor, a remote weldedcomponent, like a manway cover, may become damaged about its weld, and areplacement cover may need to be mechanically bolted over the sameunderwater. During this repair, a spotface may be electrical dischargemachined in the cover to a depth of 0.05 inches to accommodate thereplacement cover. EDM is generally used in such processes because itproduces a fine swarth that does not interfere with reactor internalsand can be executed far underwater.

Related art rotating electrode 10 may be used in a larger spotfacingassembly to EDM such a hole during a manway cover replacement or otheroperation. As shown in FIG. 1, rotating electrode 10 may rotate about acentral axis, such as on a spindle or axle (not shown) in the assembly.Several electrode segments 11A, 11B, and 11C may each be powered throughleads 12 connecting up through a brush or other non-secured connectionto a powering electrode and out to segments 11A, 11B, and 11C.Individual electrodes 13 or discharge faces may thus be powered androtated in an annular fashion across a surface to be machined. Rotatingelectrode 10 may be moved transversely about the desired spot,potentially underwater, as individual electrodes rotate and electricallydischarge machine the surface. At various points in the operation,related art rotating electrode may be replaced as electrode segments11A, 11B, 11C, etc. become worn, over potentially several hours ofdischarging away the material.

SUMMARY

Example embodiments include EDM assemblies that can be fixed to amachining surface while rotating sub-electrodes on their own axes. Thus,when discharging the sub-electrodes, a large electrode-surface interfaceis generated, and a larger amount of material is removed. Thesub-electrodes can also revolve about a shared axis while discharging,further increasing material removal and evenness of the EDM burn. Therelative motions may be achieved with planetary gears fixed with thesub-electrodes and meshing with a stationary sun gear. Severalsub-electrodes can be used in a single assembly, such as six cylindricalsub-electrodes that each rotate, and the sub-electrodes may berelatively large, such as several inches in diameter.

The sub-electrodes can also move downward from a spindle on the mountand into a surface being machined, up to several inches, to create adeep hole. For example, these operations may be used in a reactor duringa maintenance period to machine a hole for a replacement manway coverunderwater in the flooded reactor. Rotational and vertical movement canbe independently controlled with separate motors in the assembly, andpower and controls may be provided remotely through an underwaterconnection. The installation and use of example embodiments, includingthe securing of an electrode to the mount, may occur underwater.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Example embodiments will become more apparent by describing, in detail,the attached drawings, wherein like elements are represented by likereference numerals, which are given by way of illustration only and thusdo not limit the terms which they depict.

FIG. 1 is an illustration of a related art rotating electrode.

FIG. 2 is an illustration of an example embodiment electrical dischargemachining assembly

FIG. 3 is an illustration of an example embodiment planetary electrode.

FIG. 4 is a cross-sectional schematic of the example embodimentelectrical discharge machining assembly and planetary electrode.

DETAILED DESCRIPTION

Because this is a patent document, general, broad rules of constructionshould be applied when reading it. Everything described and shown inthis document is an example of subject matter falling within the scopeof the claims, appended below. Any specific structural and functionaldetails disclosed herein are merely for purposes of describing how tomake and use examples. Several different embodiments and methods notspecifically disclosed herein may fall within the claim scope; as such,the claims may be embodied in many alternate forms and should not beconstrued as limited to only examples set forth herein.

It will be understood that, although the ordinal terms “first,”“second,” etc. may be used herein to describe various elements, theseelements should not be limited to any order by these terms. These termsare used only to distinguish one element from another; where there are“second” or higher ordinals, there merely must be that many number ofelements, without necessarily any difference or other relationship. Forexample, a first element could be termed a second element, and,similarly, a second element could be termed a first element, withoutdeparting from the scope of example embodiments or methods. As usedherein, the terms “and,” “or,” and “and/or” include all combinations ofone or more of the associated listed items unless it is clearlyindicated that only a single item, subgroup of items, or all items arepresent. The use of “etc.” is defined as “et cetera” and indicates theinclusion of all other elements belonging to the same group of thepreceding items, in any “and/or” combination(s).

It will be understood that when an element is referred to as being“connected,” “coupled,” “mated,” “attached,” “fixed,” etc. to anotherelement, it can be directly connected to the other element, orintervening elements may be present. In contrast, when an element isreferred to as being “directly connected,” “directly coupled,” etc. toanother element, there are no intervening elements present. Other wordsused to describe the relationship between elements should be interpretedin a like fashion (e.g., “between” versus “directly between,” “adjacent”versus “directly adjacent,” etc.). Similarly, a term such as“communicatively connected” includes all variations of informationexchange and routing between two electronic devices, includingintermediary devices, networks, etc., connected wirelessly or not.

As used herein, the singular forms “a,” “an,” and the are intended toinclude both the singular and plural forms, unless the languageexplicitly indicates otherwise. Indefinite articles like “a” and “an”introduce or refer to any modified term, both previously-introduced andnot, while definite articles like “the” refer to a samepreviously-introduced term; as such, it is understood that “a” or “an”modify items that are permitted to be previously-introduced or new,while definite articles modify an item that is the same as immediatelypreviously presented. It will be further understood that the terms“comprises,” “comprising,” “includes,” and/or “including,” when usedherein, specify the presence of stated features, characteristics, steps,operations, elements, and/or components, but do not themselves precludethe presence or addition of one or more other features, characteristics,steps, operations, elements, components, and/or groups thereof.

The structures and operations discussed below may occur out of the orderdescribed and/or noted in the figures. For example, two operationsand/or figures shown in succession may in fact be executed concurrentlyor may sometimes be executed in the reverse order, depending upon thefunctionality/acts involved. Similarly, individual operations withinexample methods described below may be executed repetitively,individually or sequentially, to provide looping or other series ofoperations aside from single operations described below. It should bepresumed that any embodiment or method having features and functionalitydescribed below, in any workable combination, falls within the scope ofexample embodiments.

As used herein, “axial” and “vertical” directions are the same up ordown directions oriented along the major axis of a nuclear reactor,often in a direction oriented with gravity. “Transverse” directions areperpendicular to the “axial” and are side-to-side directions oriented ina single plane at a particular axial height.

The Inventors have newly recognized a need to greatly increase electroderesilience and reduce the number of electrode exchanges that may berequired in heavy electrical discharge machining (EDM). Particularly, ina commercial nuclear reactor during outage periods, repairs and otheroperations must be executed quickly to return the plant to anoperational state as soon as possible. There is also a need to producelarge and deeper holes or cuts in remote environments, which onlyfurther increases wear on electrodes, especially a single, thin annularelectrode as shown in FIG. 1. Example embodiments described belowuniquely enable solutions to these and other problems discovered by theInventors.

The present invention is rotatable electrodes for EDM, and assembliesand methods for using the same. In contrast to the present invention,the few example embodiments and example methods discussed belowillustrate just a subset of the variety of different configurations thatcan be used as and/or in connection with the present invention.

FIG. 2 is an illustration of an example embodiment EDM assembly 100. Asshown in FIG. 2, assembly 100 includes linear mount 120 in whichelectrode assembly 115 may be moveably nested. Linear mount 120 may havea bridge-like shape with legs that permit its fixture to an area forEDMing and a top portion with controls and power for moving electrodeassembly 115. Linear mount 120 may be positioned by a hoist ring 121 onone or more sides of its legs or any other connection point. In thisway, example embodiment EDM assembly may be positioned and secured inremote and even underwater positions, such as over a manway coversubmerged in a nuclear reactor requiring repair. Umbilical port 125 mayconnect data, power, and/or controls to/from a remote operator from/toassembly 100, and/or any other form of communicative and powerconnection may be used in assembly 100.

Electrode assembly 115 includes example embodiment planetary electrode200 (FIG. 3) moveable with respect to linear mount 120, at least in avertical direction and rotatably on a vertical axis. Electrode assembly115 may house planetary electrode 200 in one or more electrode guards111 that prevent debris or foreign objects interfering with sides or topof planetary electrode 200. Insulator 110 may be positioned interior toelectrode assembly 115 to prevent electrical discharge between assembly115 and electrode 200. Alternatively, electrode assembly 115 may includeonly planetary electrode 200, such that electrode 200 is not largelysurrounded by electrode guards 111

FIG. 3 is an illustration of example embodiment planetary electrode 200in isolation, although electrode 200 is useable in example embodimentEDM assembly 100 discussed above. As shown in FIG. 3, planetaryelectrode 200 includes several electrode bodies 201 arranged in acircular orbit; however, other orbit and electrode shapes are useable inexample embodiments. Similarly, while six cylindrical electrode bodies201 are shown in FIG. 3, any number and shape of electrode bodies may beused. Electrode bodies 201 rotate about individual vertical axes throughtheir respective centers and also revolve about a vertical axis througha center of planetary electrode 200. These motions are shown by arrowsin FIG. 3.

The combined revolutionary and rotational motion of electrode bodies 201presents increased electrode-EDM-surface relative motion as well as moreelectrode surface being used in EDM, improving material removal andreducing wear on electrode bodies 201. For example, compared to relatedart rotating electrode 10 in FIG. 1, example embodiment planetaryelectrode 200 in a same spotface area may present over twice the surfacearea to the spotface area. As an example, electrode bodies may each becylindrical with approximately 7-8 inch diameters and formed ofgraphite, silver tungsten, and/or any other EDM-appropriate material.The reminder of assembly 100 and electrode 200 may be fabricated ofmaterials that are compatible with a nuclear reactor environment,including materials that maintain their physical characteristics whenexposed to high-temperature materials and radiation, such as stainlesssteels and iron alloys, aluminum alloys, zirconium alloys, etc.

The revolutionary and rotational movement of electrode bodies 201 may beaccomplished by fixing electrode bodies 201 on planetary gears 205 thatmesh with sun gear 204. Top guide 207 and bottom guide 206 may fixelectrode bodies 201 in an orbit about sun gear, and as bodies 201revolve, planetary gears 205 meshed with sun gear 204 cause bodies 201to rotate proportionally. Electrical power may be further providedthrough top guide 207 ad/or planetary gears 205 to charge electrodebodies 201 while rotating and revolving. Of course, other mechanicalconfigurations are useable with example embodiment electrode 200 toachieve revolution and/or rotation of the same.

FIG. 4 is a cross-sectional illustration of example embodiment EDMassembly 100 showing example embodiment planetary electrode 200 moveablein the same when mounted to surface 1 to be EDMed. As shown in FIG. 4,central spindle 150 connects to example embodiment planetary electrode200 to rotate electrode 200 and move electrode 200 in a verticaldirection. For example, spindle 150 may form a ball and screw connectionwith linear mount 120, and stepper motor 160 may rotate spindle 150 viatiming belt 161 to cause the vertical displacement of spindle 150 andelectrode 200 due to the ball and screw connection. Spindle 150 mayconnect to electrode 200 via top guide 207 or any other component ofelectrode 200. Top guide 207 may be rotated with a separate steppermotor 170 while sun gear 204 does not rotate, causing the revolutionaryand rotational motion of electrode bodies 201.

As seen, electrode 200 may be vertically lowered against surface 1 forEDM while linear mount 120 remains stationary. The vertical depth of theEDM may be adjusted based on the application and amount of materialneeded to be removed. For example, a hole of several inches, such as a1.85-inch deep spotface, may be formed with similar vertical movement ofelectrode 200 in example embodiment assembly 100. The increasedinterface area and larger wear distribution across electrode bodies 201will remove material in the spotface up to 2.3 times faster than relatedart electrodes, with a reduced number of electrode changes, potentiallyup to half the necessary changes, due to wear. The combined fasterEDMing and fewer stoppages for electrode changes are expected to speedseveral tasks using example embodiment EDM assembly 100, reducingdowntime and allowing operations to resume faster.

Example embodiments and methods thus being described, it will beappreciated by one skilled in the art that example embodiments may bevaried and substituted through routine experimentation while stillfalling within the scope of the following claims. For example, anynumber of electrodes and sizes aside from those shown can be used inexample embodiment EDM assemblies, simply through proper dimensioningand positioning. Such variations are not to be regarded as departurefrom the scope of these claims.

What is claimed is:
 1. An assembly for electrical discharge machining,comprising: a mount configured to secure about a surface to be machined;and an electrode rotatably coupled to the mount, wherein the electrodeincludes a plurality of electrode bodies, wherein each of the electrodebodies is configured to rotate about a vertical axis internal to acorresponding electrode body; a first stepper motor configured to movethe electrode vertically; and a second stepper motor configured torotate the electrode bodies about the vertical axis internal to acorresponding electrode body, wherein the electrode is rotatablyconnected to a spindle of the mount on which the electrode is verticallymoveable, and wherein the first stepper motor is configured to rotatethe spindle so as to cause the vertical movement through aball-and-socket connection.
 2. The assembly of claim 1, wherein theplurality of electrode bodies are further configured to all revolveabout a vertical axis central to the electrode.
 3. The assembly of claim2, wherein each of the electrode bodies are fixed with a planetary gear,and wherein the electrode includes a sun gear meshed with the planetarygears.
 4. The assembly of claim 1, wherein the electrode is furtherconfigured to vertically move relative to the mount.
 5. The assembly ofclaim 4, wherein the electrode is rotatably connected to a spindle ofthe mount on which the electrode is vertically moveable.
 6. The assemblyof claim 4, wherein the plurality of electrode bodies are furtherconfigured to all revolve about a vertical axis central to theelectrode.
 7. The assembly of claim 6, wherein each of the electrodebodies are fixed with a planetary gear, and wherein the electrodeincludes a sun gear meshed with the planetary gears.
 8. The assembly ofclaim 1, wherein the plurality of electrode bodies includes sixcylindrical electrode bodies.
 9. A method of electrically dischargemachining a surface, the method comprising: securing an electrode to thesurface with a mount, wherein the securing occurs underwater; androtating a plurality of electrode bodies in the electrode each about avertical axis internal to a corresponding electrode body whiledischarging an electrical current through the plurality of electrodebodies.
 10. The method of claim 9, further comprising: revolving theplurality of electrode bodies about a vertical axis central to theelectrode while discharging the electrical current through the pluralityof electrode bodies.
 11. The method of claim 10, wherein each of theelectrode bodies are fixed with a planetary gear, and wherein theelectrode includes a sun gear meshed with the planetary gears.
 12. Themethod of claim 9, further comprising: vertically moving the electroderelative to the mount while discharging the electrical current throughthe plurality of electrode bodies.
 13. The method of claim 12, whereinthe electrode is rotatably connected to a spindle of the mount on whichthe electrode is vertically moveable.
 14. The method of claim 9, whereinthe plurality of electrode bodies includes six cylindrical electrodebodies.
 15. A method of electrically discharge machining a surface, themethod comprising: securing an electrode to the surface with a mount;and rotating a plurality of electrode bodies in the electrode each abouta vertical axis internal to a corresponding electrode body whiledischarging an electrical current through the plurality of electrodebodies, wherein the surface is a manway cover in a nuclear reactor, andwherein the method is performed entirely underwater.
 16. The method ofclaim 15, further comprising: vertically moving the electrode over 1.5inches relative to the mount and into the surface while discharging theelectrical current through the plurality of electrode bodies so as toremove at least 1.5 inches of the surface.
 17. The method of claim 16,further comprising: revolving the plurality of electrode bodies about avertical axis central to the electrode while discharging the electricalcurrent through the plurality of electrode bodies.
 18. The method ofclaim 15, wherein the method is performed entirely during a maintenanceoutage of the nuclear reactor.